The biosynthesis of visual pigment (rhodopsin) and phospholipids and their assembly into rod outer segment disc membranes is being studied in frogs and rats. The interrelationship of phospholipids and rhodopsin in the assembly of the rod discs is being investigated by a combination of radiobiochemical and autoradiographic techniques. These investigations are being conducted using normal rats, and rats suffering from hereditary retinal degeneration (RCS rats). The metabolism of the pigment epithelium in relationship to the phagocytosis of rod outer segments is being studied in normal and RCS rats. The site and mode of attachment of vitamin A to opsin during the biosynthesis of this macromolecule is being investigated.